Production of vinyl acetate

ABSTRACT

A PROCESS FOR THE PRODUCTION OF VINYL ACETATES BY THE VAPOUR PHASE CATALYTIC REACTION OF ETHYLENE, OXYGEN AND ACETIC ACID EMPLOYING A PLATINUM GROUP METAL CATALYST SUPPORTED ON TITANIA OR MIXTURES OF TITANIA AND AN ALKALI METAL SILICATE.

United States Patent 3,592,840 PRODUCTION OF VINYL ACETATE Peter JohnDurston, Thames Ditton, England, assrgnor to BP Chemicals (U.K.)Limited, formerly known as Distillers Chemicals and Plastics Limited,London, England No Drawing. Filed May 17, 1967, Ser. No. 639,067 Claimspriority, application Great Britain, June 7, 1966, 25,318/ 66 Int. Cl.C07c 67/04 US. Cl. 260-497A 4 Claims ABSTRACT OF THE DISCLOSURE Aprocess for the production of vinyl acetates by the vapour phasecatalytic reaction of ethylene, oxygen and acetic acid employing aplatinum group metal catalyst supported on titania or mixtures oftitania and an alkali metal silicate.

The present invention relates to the production of esters of unsaturatedalcohols such as vinyl acetate.

Processes for the production of esters of unsaturated alcohols such asvinyl acetate by the oxidation of olefines such as ethylene withmolecular oxygen in a mixture containing acetate ion and acetic acid inthe presence of a catalyst comprising a platinum group metal are known.Such reactions may be carried out in the liquid or vapour hase.

p According to the present invention, a process for the production ofvinyl acetate comprises reacting in the vapour phase at an elevatedtemperature ethylene, a molecular oxygen-containing gas and acetic acidin the presence of a catalyst comprising a platinum group metaldeposited on titania, an alkali metal, alkaline earth metal, zinc,cobalt, nickel or iron silicate, or mixtures thereof or mixtures oftitania and/ or the metal silicates with silica as support.

By the term platinum group metal is meant any of the metals platinum,palladium, rhodium, ruthenium, osmium or iridium.

The platinum group metal catalyst may be for instance elemental metale.g. palladium or rhodiu or the oxides or salts of such metals e.g.palladous chloride. When the catalyst is elemental metal it is preferredto prepare it by reduction of a salt of the metal with hydrazine hydratein alkaline solution e.g. sodium in potassium hydroxide.

The acetic acid may be supplied to the reaction in vapour form bypassage of the gaseous ethylene through a reservoir of the liquid acidso as to saturate the olefine with the acid vapour, or the acid ispumped to the reactor via a vaporiser.

The molecular oxygen containing gas may be oxygen as such, air ormixtures of oxygen with air.

The process may be carried out at atmospheric, subatmospheric orsuper-atmospheric pressure, preferably the process is efiected underpressures in the range 1 to 50 atmospheres especially in the range 2 to20 atmospheres. Suitable reaction temperatures are 50 to 250 C.,temperatures in the range 100 to 200 C. being preferred.

The use of titania or titania-silica or titania-silicate mixtures ascatalyst supports has the advantage that the catalyst may be readilyreactivated. Thus, it has been found that after a time, the rate ofproduction of esters such as vinyl acetate over a given catalyst falls,and it is then found that appreciable amounts of higher boilers havebecome adsorbed on the catalyst. These can be removed and the vinylacetate production rate restored completely to the initial value by asecond embodiment of the present invention namely heating the catalystwith an alkaline medium such 3,592,840 Patented July 13, 1971 as causticsoda or sodium carbonate solution. Other methods of reactivation includeheating in air, steam or inert gas with or without acetic acid or undervacuum.

In operation the process may be carried out for instance by passing thegaseous olefine together with acetic acid vapour and oxygen over theplatinum group metal catalyst contained in a heated reaction tube. Theacetate ester product which may contain by-products may be recoveredfrom the reaction gases by condensation or solvent extraction andfractional distillation of the condensate or extract. Excess olefine maybe re-cycled tothe reactor.

The process of the invention is further illustrated by the followingexamples:

EXAMPLE 1 A 10% palladium/titania catalyst was prepared by adding PdClin 50% hydrochloric acid solution to titania, the catalyst was dried atC. and reduced with alkaline hydrazine. When ethylene (0.3 mole/hr.),oxygen (0.06 mole/hr.), and acetic acid (0.08 mole/hr.) were passed overthis catalyst in a thermostatically controlled reactor at 140 C. a rateof vinyl acetate production of 0.10 mole/ l./hr. was observed for 70hours. This rate fell to 0.03 mole/l./hr. after 94 hours. The feeds weretemporarily discontinued whilst the catalyst was treated with boiling 2N sodium hydroxide solution. This treatment increased the rate to 0.30mole/L/hr. for the next 176 hours but it fell again to 0.01 mole/l./hr.;further treatment with boiling caustic soda restored the rate of 0.30mole/L/hr. of vinyl acetate maintained for a further 362 hours.

EXAMPLE 2 A 5% palladium on cobalt silicate catalyst was prepared bymixing cobalt nitrate [Co(NO (27.3 g.) in water (20 ml.) with sodiummetal silicate (21.2 g.) and stirring well. After drying at 140 C. for12 hours, palladium chloride 1.65 g.) in 50% hydrochloric acid wasadded, and after further drying at 140 C. the catalyst was reduced withalkaline hydrazine.

The reaction was carried out at C. with flow rates of ethylene (0.36mole/hr.) oxygen (0.06 mole/hr.) and acetic acid (0.13 mole/hr.). A rateof vinyl acetate production of 0.08 mole/l./hr. was obtained for 77hours and treatment of the catalyst with boiling caustic soda increasedthe rate to 0.26 mole/l./hr. for a further 50 hours.

EXAMPLE 3 A 5% palladium on a mixed titania/sodium meta silicatecatalyst was prepared by mixing equal amounts of titania and sodium metasilicate and adding enough water to make a slurry. This was well mixedand dried at 140 C. The palladium was then added as already described.

The catalyst gave 0.07 mole/L/hr. of vinyl acetate after 2 hours but therate steadily increased to give 0.30 mole/ l./ hr. after 20 hours.Thereafter it increased to 0.67 mole/ l./hr. which was maintained for afurther 168 hours.

As a comparison a 5% palladium on aluminium silicate catalyst (that is acatalyst not in accordance with the present invention) was prepared bythe addition of palladium chloride in 50% hydrochloric acid solution toaluminium silicate. The resulting slurry was well mixed and dried at 140C. the palladium chloride then being reduced with alkaline hydrazine aspreviously described.

The catalyst gave 0.07 mole/l./hr. of vinyl acetate after 2 hours butthe rate fell to 0.037 mole/l./hr. after 23 hours.

EXAMPLE 4 A catalyst containing 3.5% Pd on 1:1 SiO /Ti0 was prepared byadding titanic chloride, with constant stirring to a solution of sodiummetasilicate at 80 C. and which had been brought to pH 7 by the additionof hydrochloric acid. The weights of titanic chloride and of sodiummetasilicate were such as to give a 1:1 ratio w./w. of Si to TiO Theresultant precipitate was stirred for 15 minutes at 80 C. and thenfiltered, washed with distilled Water until free of acid and dried at140 C. The dry solid was made into a slurry with distilled water, heatedto 80 C. and mixed with a solution of palladium chloride (PdCl in 50%HCl. After cooling to room temperature, the solid was filtered from theexcess palladium chloride solution, reduced with alkaline hydrazine anddried at 140 C.

When ethylene (0.3 mole/hr.), oxygen (0.06 mole/ hr.) and acetic acid(0.08 mole/hr.) were passed over this catalyst at 140 C. a rate of vinylacetate production of 0.56 mole/litre/hour was obtained for 1029 hours,without regeneration or any reduction in the catalysts activity.

EXAMPLE 5 A 7.7% palladium on a mixed (1:1) titania/silica catalyst wasprepared by dissolving sodium metasilicate in water and precipitatingthe silica by the addition of concentrated hydrochloric acid until thepH was 7. Titanium tetrachloride was added to the solution and titaniaprecipitate. The mixture was stirred Well, filtered, and dried.Palladium chloride was then impregnated on the support and reduced withalkaline hydrazine.

The catalyst gave 1.42 mole/L/hr. of vinyl acetate after 18 hours at 140C., and the yield was 1.00 mole/l./ hr. after 67 hours.

I claim:

1. A process for the production of vinyl acetate which comprisesreacting in the vapor phase at an elevated temperature above 50 C.ethylene, a molecular oxygen-containing gas and acetic acid in thepresence of a catalyst comprising an elemental platinum group metalselected from the group consisting of platinum, palladium, rhodium,ruthenium, osmium or iridium, deposited on a support material selectedfrom the group consisting of titania, or mixtures of titania and analkali metal silicate.

2. A process as claimed in claim 1 wherein the catalyst comprises anelemental platinum group and the pressure and temperature in the reactorare elevated.

3. A process as claimed in claim 1 carried out under pressures of 1 to50 atmospheres absolute.

4. A process as claimed in claim 1 carried out at an elevatedtemperature of 50 to 250 C.

References Cited UNITED STATES PATENTS LEWIS GOTTS, Primary Examiner V.GARNER, Assistant Examiner US. Cl. X.R.

